The present invention relates to a portable transceiver used as a portable unit in a cellular telephone system and to a transfer system for electronic serial numbers (ESN's) used by portable transceivers and, more particularly, to a portable transceiver and an ESN transfer system capable of preventing ESN's used in the transceivers from being duplicated.
Each portable transceiver used as a mobile unit in a car telephone system is assigned a unique ESN to identify or specify the transceiver. The transceiver, when initiating a call to the base station, sends out a call initiation signal including the ESN assigned to it. When receiving an arriving call from the base station, the portable transceiver responds with an arriving call response signal including its ESN. An ESN is required to be unique to each individual transceiver, but not to be duplicated among a plurality of transceivers. The way in which an ESN is assigned to each individual transceiver in compliance with this requirement is left to the choice of the manufacturer of the transceivers.
A first example of a method conventionally adopted to prevent the duplication of the same ESN is to use a PROM into which no rewriting is possible (a one-time PROM) as a memory for the storage of the ESN. In a portable transceiver using this method, when the panel or the apparatus (hereinafter-collectively referred to as the panel) on which such a one-time PROM is mounted is to be replaced to remedy trouble or for any other reason, the one-time PROM fitted to the panel to be replaced should be shifted to the new panel. However, along with the size reduction of portable transceivers, the replacement of the one-time PROM has become increasingly difficult and time-consuming.
A second conventional method is to use an electronically erasable PROM (EEPROM) as a memory for the storage of the ESN. In a portable transceiver using this method, when the panel on which such an EEPROM storing the ESN is mounted is to be replaced in a maintenance procedure, the ESN should be read out of the EEPROM on the panel to be replaced and transferred to another EEPROM on the new panel. Therefore, such a portable transceiver, which involves no need to shift the EEPROM from the panel to be replaced to the new panel, has the advantage of easier maintenance over the aforementioned first example of the prior art. However, it still is not free from the risk of erroneously transferring the ESN in an EEPROM mounted on a specific panel to more than one EEPROM or of leaving the ESN unerased in the EEPROM even after the transfer of the ESN, making it difficult to ensure the protection of a specific ESN from being duplicated.
By another conventional method, an ESN transfer program for use in the transfer of the ESN stored in the EEPROM is provided on the panel itself of the portable transceiver. This is the ESN transfer method used in the KS Mobile Audio/Logic Board (made by Motorola Inc., U.S.A.) (cf. Cellular Subscriber Technical Training Manual by Motorola). By this technique, two boards on each of which an EEPROM is mounted are connected with a connecting cable, by way of which the ESN is transferred in a series of procedures. Connecting the two boards with the connecting cable, however, requires the opening of the portable transceiver's casing, entailing a correspondingly longer working time.
Whereas the replaced panel is usually repaired by its manufacturer, whether or not the cost of the panel repair is to be charged to the user is often cumulated referring to the ESN, resulting in the problem that a transfer of an ESN between a panel whose repair cost is charged to its user and another which is repaired free of charge disturbs the maintenance history management of the panel.